A Conceptual Model Showing the Enhanced Sorption and Reductive Degradation of Various Short- and Long-Chain PFAS by a Cost-Effective, Sustainable, “All-in-One” Biochar-Surfactant System (BSS)

This project will engineer a cost-effective, sustainable biocharsurfactant system (BSS) to treat per- and polyfluoroalkyl substances (PFAS)-impacted groundwater (C4–C15 anionic, cationic, and zwitterionic PFAS) via enhanced sorption and destruction by advanced reduction processes using hydrated electrons (e_aq–) (Figure 1). This proof-of-concept project has three major objectives:

1. Synthesize, characterize, and select the desirable biochar and BSS;
2. Investigate the sorption of various PFAS by the biochar and BSS; and
3. Test and optimize the effectiveness and efficiency of biochar and BSS for PFAS destruction, particularly including the most recalcitrant short-chain PFAS.

Cost-effective biochars have the capacity to sorb various short- and long-chain anionic, cationic, and zwitterionic PFAS. Hydrated electrons (e_aq–)have the power to reductively destruct PFAS toward complete defluorination. If engineered appropriately, the “all-in-one” BSS will have the synergy to sorb (preconcentrate) and destruct PFAS by e_aq– under coupled ultraviolet and ultrasound activations. Biochar key properties (e.g., surface area, pore volume, surface charge, and redox-active phenolic and quinone moieties) that will affect PFAS sorption and destruction can be rationally tuned by altering feedstock source and pyrolysis condition, in concert with appropriate pre- and post-activations. Coating the biochar with surfactant (i.e., cetyltrimethylammonium bromide [CTAB]) will further enhance PFAS preconcentration as well as prolong the longevity of e_aq– (e.g., CTAB micelles), which is critical for PFAS destruction. In addition, cavitation bubbles and e_aq– generated during ultrasonication treatment will further contribute to enhanced PFAS sorption and destruction. Together, these advantages and attributes, if harnessed smartly, will result in a synergy of different BSS components to treat PFAS-impacted groundwater effectively and efficiently.

This project will engineer a cost-effective, “all-in-one” system that will contribute to efforts by the Department of Defense (DoD) to sustainably remediate PFAS-impacted groundwater (e.g., in the presence of recalcitrant short-chain PFAS). Due to the anticipated synergy of biochar and the surfactant (CTAB) in the sorptive fixation of a wide spectrum of PFAS, this cost-effective system will also have the potential to be used as a permeable adsorptive barrier in managing PFAS-contaminated sites in situ. The inclusion of scientists from the U.S. Environmental Protection Agency Office of Research and Development and Geosyntec (consulting industry) will facilitate the technology transfer of the project results and feedbacks to DoD stakeholders that are regular partners in the environmental regulation and remediation practice. (Anticipated Project Completion - 2024)

Lyu, X., F. Xiao, C. Shen, C.M. Park, Y. Sun, M. Flury, and D. Wang. 2022. Per- and Polyfluoroalkyl Substances (PFAS) in Subsurface Environments: Occurrence, Fate, Transport, and Research Prospect. Reviews of Geophysics, 60(3):e2021RG000765. doi.org/10.1029/2021RG000765.